Mel... try this...

First delete the avatar you have now... by telling that you don't want to have an avatar. Confirm your new settings. Log out from PC. Close down internet.
Then open internet again... log in on PC. Go to your settings and upload your new avatar....confirm.If you're lucky it will be there if you take a look in the forums. If not... Log out from PC... close internet and open them up again.... then look at one of your posts to see if the new avatar is in place.

Good luck!